The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Can You Take Mounjaro 2.5 mg Twice a Week?
No — Mounjaro is designed as a once-weekly injection only. Taking 2.5 mg twice a week (which would equal 5 mg weekly) is not an approved dosing schedule in the UK or anywhere else. Mounjaro's dose titration follows a strict schedule set by UK regulators and your prescriber, and deviating from it carries risks. If you're experiencing side effects from the starting dose or have questions about your treatment plan, speak with your GP or prescriber — they can adjust your dose safely according to NHS guidance.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Mounjaro Dosing — What the Guidelines Say
Mounjaro (tirzepatide) is prescribed as a once-weekly injection only. The approved UK dose titration schedule is:
- Weeks 1–4: 2.5 mg once weekly
- Weeks 5–8: 5 mg once weekly (if tolerated)
- Weeks 9–12: 7.5 mg once weekly (optional escalation)
- Weeks 13+: Up to 15 mg once weekly (maximum dose)
Each dose is injected on the same day each week — typically a KwikPen contains 4 weeks' supply (4 doses). The MHRA-approved prescribing information specifies at least 4 weeks on each dose before increasing. Taking 2.5 mg twice weekly would mean injecting twice in 7 days, which exceeds the approved frequency and could lead to unpredictable drug levels, increased side effects, and potential safety issues. Your prescriber will not recommend or approve this approach.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Why This Matters and What to Do Instead
If you're considering this because you're struggling with side effects at 2.5 mg, or because you want faster results, tell your prescriber — don't adjust the dose yourself. Common side effects (nausea, diarrhoea) often settle within 1–2 weeks as your body adapts. If they persist or are severe, your GP or weight management service can discuss alternatives: staying on 2.5 mg longer, switching to a different GLP-1 medication like Wegovy, or pausing treatment. If you're seeking faster weight loss, remember that clinical trials show sustainable results come from combining medication with a reduced-calorie diet and increased physical activity. Use our GLP-1 weight loss calculator to see realistic projections at approved doses, and talk honestly with your prescriber about your goals and concerns.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What if I'm having bad side effects on 2.5 mg Mounjaro — can I split the dose?
No — splitting or dividing doses is not approved and could be unsafe. Tell your prescriber about side effects instead. Most settle within 1–2 weeks. If they don't, your prescriber may recommend staying on 2.5 mg longer, switching medications, or other adjustments. Never change your dose without guidance.
Can I take Mounjaro more frequently to lose weight faster?
No. Mounjaro works on a strict once-weekly schedule approved by UK regulators. Taking it more frequently will not speed up weight loss and may cause serious side effects or reduce effectiveness. Sustainable weight loss requires time, medication consistency, diet, and exercise — not faster injections.
What's the difference between Mounjaro and Wegovy dosing schedules?
Mounjaro is once-weekly (starting 2.5 mg, maximum 15 mg). Wegovy is also once-weekly but starts at 0.25 mg and goes up to 2.4 mg. Both use gradual dose titration over weeks. Neither can be taken more frequently than once weekly. If Mounjaro's side effects are problematic, your prescriber might discuss switching to Wegovy instead.
How long do I stay on the 2.5 mg starting dose?
The approved schedule is 4 weeks minimum on 2.5 mg before increasing to 5 mg (if tolerated). If side effects are significant, your prescriber may keep you on 2.5 mg for longer — even 8 weeks or more — to let your body adapt. Never rush escalation or try to speed it up by injecting more frequently.
Is there any scenario where taking Mounjaro twice weekly is safe?
No — the UK approved prescribing information specifies once-weekly dosing only. There is no clinical trial data, no NHS guidance, and no prescriber approval for twice-weekly Mounjaro dosing. Doing this would be taking the medication off-label and outside approved safety parameters. Always follow your prescription exactly as written.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.